University of Hawai`i

Botany Department

          Marine Algae of Hawai`i

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Gracilaria tikvahiae

McLachlan 1987

Invasive Alien



Class Order Family
Rhodophyta >Rhodophyceae Ceramiales Rhodomelaceae

Click on pictures for larger images




Gracilaria tikvahiae was introduced for commercial mariculture to relieve the overharvesting of the native G. parvispora. Containment to mariculture sites have been fairly successful, but its opportunistic
nature makes it a potentially successful invasive species.


















Herbarium sheets of Gracilaria tikvahiae
showing morphological variations.







Thallus 12-15 cm tall, comprised of finely branched clumps, irregularly branched, 1mm wide. Axes compressed or flattened,with short laterals bering more slender than axes with spinous branchlets. Branching mostly dichotomous, but can be highly irregular, with dichotomous below, alternate above and dichotomous at apices. Apices tapered and pointed, often unevenly forked with one side longer than the other.  In the wild, the plant can range from dark green to shades of red and brown.


The morphology of this alga is highly variable. Plants grown commercially are often completely dichotomously branched with axes and branches of nearly the same diameter throughout. Cultured plants are often very dark green to nearly black.


Structural Features

Medullary cells irregular, 70-270 mm diam. Cortex is 2-3 cells thick; surface cells round to angular, 5-13 mm diam., densely pigmented. Tetrasporangia oval to spherical, 10-35 mm diam., 17-45 mm long, cruciately divided, scattered in surface layers. Spermatangia in sori, scattered. Cystocarps hemispherical, to 1mm diam., numerous; carposporangia spherical to oval, 15-40 mm diam.



Gracilaria tikvahiae is found intertidal, less that 1 meter, attached to limestone and basalt substrates. In the Caribbean and Florida where it is very common, G. tikvahiae is found in protected and high-energy intertidal habitats in estuaries and bays to 10 meters deep. This plant may grow unattached or attached to rocks or coral rubble.



Hawai‘i:  Near Oceanic Institute, Makapu’u, O‘ahu.

Mechanism of Introduction:  This species was brought to the Hawaiian Islands from Florida in 1987 for commercial mariculture.

Worldwide:  Nova Scotia, Western Atlantic, Canada to Florida.



Gracilaria tikvahiae has a widespread distribution throughout the world, and is often associated with eutrophic conditions. As demonstrated by its temperate and tropical locations, it is able to tolerate large environmental variations in levels of nitrogen, irradiance and temperature. This red alga has also been found to have a high nutrient uptake efficiency, making it a successful invasive in many types of marine environments. Because of its hardiness and greater adaptability than the Hawaiian endemic species, G. tikvahiae has the potential to be an invasive species on Hawaiian reefs.


Gracilaria tikvahiae was brought to the Hawaiian islands in 1987 to relieve the dwindling availability of G. coronopifolia and G. parvispora, the two most popular edible species of the genus. This species has a high growth rate under non-limiting irradiance and nutrient conditions. It also has the ability to store large amounts of dissolved nitrate and nitrite, enabling it to continue growth in conditions of fluctuating nitrogen availability. Productivity of G. tikvahiae can be as high as any terrestrial crop on earth and is being studied for its viability as an agar weed.


Established populations of Gracilaria tikvahiae have not been found in the wild in Hawai‘i, although occasional escapes have been reported. This species has not reproduced sexually in mariculture but does quickly reproduce vegetatively, and has demonstrated successful invasive characteristics elsewhere. It’s success on intertidal areas with moderate water motion makes it a potential competitor of the two already stressed endemic species, G. coronopifolia and G. parvispora. With the growing concern of eutrophic conditions developing along Hawaiian coastlines due to coastline development and G. tikvahiae’s opportunistic nature, this species needs to be carefully handled for mariculture and wild populations should be reported and monitored.


Abbott, I.A., 1999. Marine Red Algae of the Hawaiian Islands. Bishop Museum Press, Honolulu, Hawai‘i.

Doty, M.S. 1986. Experiments with Gracilaria in Hawai‘i, 1983-1985. Hawai‘i Botanical Science Paper, no. 46, University of Hawai‘i, Honolulu, Hawai‘i.

Littler, D.S. and Mark M., 2000. Caribbean Reef Plants. OffShore Graphics, Washington, D.C.

Peckol, P., B. Demeo-Anderson, J. Rivers, I. Valiela, M. Maldonnado, and J. Yates, 1994. Growth, nutrient uptake capacities and tissue constituents of the macroalgae Cladophora vagabunda and Gracilaria tikvahiae related to site-specific nitrogen loading rates. Marine Biology 121:

Schneider, D.W, and R.B. Searles, 1991. Seaweeds of the Southeastern United States. Duke University Press, London, England.


 Web Pages

Marine Invasives in Hawai‘i:

The Indian River Lagoon Species Inventory:



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